Hierarchical modulation (HM) technology is used to transmit different data streams together, for example, a first data stream and a second data stream. From the point of view of constellation diagram, hierarchical modulation modulates an upgrade constellation (namely second data stream) on the basis of a primary constellation (namely first data stream).
FIG. 1 shows a kind of constellation map of 16QAM hierarchical modulation in prior art. This constellation map includes 16 constellations as shown by 16 black points. Any modulation symbol, which includes 4 bits, can be mapped into one of the 16 constellations. The front two bits in the modulation symbol correspond to a first data stream, while the last two bits correspond to a second data stream. The constellations corresponding to the modulation symbols of the same first data stream are located in the same quadrant. Such 16QAM hierarchical modulation may be considered as the sum of two QPSK constellations, wherein a first data stream corresponds to a primary QPSK constellation as shown by four diagonal circles, while a second data stream corresponds to an upgrade QPSK constellation as shown by four constellations in each quadrants (relative to the diagonal circle in the quadrant).
Dirty Paper Coding (DPC) modulation technology has a constellation mapping feature similar to hierarchical modulation, constellation map of which may also be consider as the sum of a primary constellation and an upgrade constellation. In the prior art, a technology scheme has been proposed that the data stream of unicast service and the data stream of multimedia broadcast service (MBMS) are transmitted together based on the Dirty Paper Coding modulation technology in the Orthogonal Frequency Division Multiplexing (OFDM) system, wherein, the unicast service data stream corresponds to a first data stream, while the MBMS data stream corresponds to a second data stream. Such technology scheme is based on the following assumption: Multiple base stations work on a single frequency network (SFN) manner for MBMS data stream.
However, there also exists a need for the technology scheme that multiple data streams (e.g., unicast service data stream and MBMS data stream) are transmitted together in case of single cell network environment.